1. Field
The present disclosure relates to a resin-framed membrane-electrode assembly for a fuel cell.
2. Description of the Related Art
Typical solid polymer electrolyte fuel cells use polymer electrolyte membranes formed of polymer ion exchange membranes. A fuel cell includes a membrane-electrode assembly (MEA) constituted by a polymer electrolyte membrane, an anode electrode disposed on one side of the polymer electrolyte membrane, and a cathode electrode disposed on the other side of the polymer electrolyte membrane. The anode electrode and the cathode electrode each include a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon).
A membrane-electrode assembly sandwiched between separators (bipolar plates) constitutes a fuel cell. A desired number of fuel cells are stacked to form, for example, an onboard fuel cell stack to be used in vehicles.
The membrane-electrode assembly may come in a form of a so-called stepped MEA in which one of the gas diffusion layers is designed to be have smaller planar dimensions than the polymer electrolyte membrane, and the other gas diffusion layer is designed to have the same planar dimensions as the polymer electrolyte membrane. In order to reduce the amount of a relatively expensive polymer electrolyte membrane used and protect the polymer electrolyte membrane which is thin and has a low strength, a resin-framed MEA having a built-in resin frame member around the outer perimeter is used.
An example of the resin-framed MEA is a membrane-electrode assembly disclosed in Japanese Unexamined Patent Application Publication No. 2007-66766. According to this membrane-electrode assembly shown in FIG. 8, an anode catalyst layer 2a and an anode gas diffusion layer 2b both having the same external dimensions as a membrane 1 are disposed on one side of the membrane 1. A cathode catalyst layer 3a and a cathode gas diffusion layer 3b both having smaller external dimensions than the membrane 1 are disposed on the other side of the membrane 1. As a result, a stepped MEA 4 is constructed.
The anode gas diffusion layer 2b is designed to have a larger area than the cathode gas diffusion layer 3b. The membrane 1 has an outer perimeter portion located at the cathode gas diffusion layer 3b side, and the outer perimeter portion is bonded to a gasket structure 5 with a bonding part 6.
According to this patent document, the outer perimeter portion (flat surface) of the membrane 1 located at the cathode gas diffusion layer 3b side is bonded to a flat surface of an inner perimeter thin portion 5a of the gasket structure 5 with the bonding part 6 which has a frame-like planar shape.